1. Field of the Invention
The present general inventive concept relates to a color prism separating and synthesizing incident light according to wavelength ranges and a projection-type image display apparatus employing the color prism, and more particularly, to a color prism structured to separate incident light into four-color beams and to synthesize the incident four-color beams and a projection-type image display apparatus employing the color prism.
2. Description of the Related Art
In general, projection-type image display apparatuses create a color image by projecting an image, which has been formed by an image forming device, such as a liquid crystal display or a digital micromirror device, onto a screen using an illumination unit. Projection-type image display apparatuses are classified into a reflection type and a transmission type according to the type of an image forming device, and also classified into a single-panel type and a three-panel type according to the number of image forming devices used.
The present general inventive concept relates to a three-panel reflective projection-type image display apparatus. A projection-type image display apparatus is disclosed in U.S. Pat. No. 6,704,144, published on Mar. 9, 2004, entitled “a projection color separation prism assembly compensated for contrast enhancement and implemented as reflective imager.”
The projection-type image display apparatus disclosed in U.S. Pat. No. 6,704,144 includes a prism assembly having three triangular prisms. The three triangular prisms are in contact with one another, and two contact surfaces of the three triangular prisms are coated with color separation filtering films. Three reflective liquid crystal on silicon (LCOS) displays are disposed to face two outer surfaces of the three triangular prisms.
Accordingly, white light emitted from a light source and incident on the prism assembly is separated according to wavelength into red, blue, and green beams after passing through the color separation filtering films. The separated beams are respectively incident on the three reflective LCOS displays. The three reflective LCOS displays respectively modulate the red, blue, and green beams by pixels to form images, and reflects the images to the prism assembly. The reflected images are synthesized, and then pass through a polarization beam splitter disposed between the light source and the prism assembly and travel toward a projection lens unit. Accordingly, the red, blue, and green beams are synthesized and projected onto a screen, thereby forming a full color image.
In the meantime, the projection-type image display apparatus forms the full color image using the LCOS displays. Hence, a color gamut is restricted to lie within a triangle shown in FIG. 1.